The present invention relates to medical implants formed of a material including a metal matrix composite and to methods of implanting the implants into patients in need of treatment. The implants according to the present invention can be used to treat either chronic or acute conditions.
Currently, natural articulating bone joints and related bone structures can be replaced by ceramic, polymeric, or metallic components or a combination thereof. For example, articulating joints such as the knees, hips, and intervertebral discs can be replaced with artificial joints. It is important that the artificial joints exhibit good biocompatibility plus favorable wear characteristics, minimize any abraded or worn surfaces, and minimize the release of accompanying debris into surrounding tissues. Typically, patients undergoing hip or knee replacement are in their sixth decade of life or older. Their joint defect, disorder, and/or deterioration can occur because of a chronic condition that has become debilitating such as arthritis or osteoporosis, trauma causing a disruption in the normal joint, or degeneration as a result of the natural aging process of a patient. Current orthopedic implants typically have a useable life span of about 15 to 20 years and may perform acceptably for older patients. These implants may not need replacement during the patient's life span. However, younger patients need such devices for longer time frames. The younger patients are also more active. It is not unexpected that implants or replacement joints in younger patients are subjected to greater stress and more motion cycles than those in older patients. Conventional implants may need to be revised after some period of use in younger patients or even in active, older patients. It is desirable that the initial replacement joints survive longer periods of use (up 50 or 60 years) and withstand greater stress or strain than the present implants to avoid the likelihood of revisitation and a replacement, which is obviously a highly undesirable consequence.
It is equally important to minimize any adverse or toxicological problems associated with production of debris material from wear of the implant's articulating surfaces. Consequently, metallic implants are made of wear-resistant, physiologically-acceptable materials such as CoCr alloys.
Some metallic implants may exhibit acceptable wear characteristics; however, the same materials may also exhibit poor imaging characteristics under commonly used diagnostic imaging techniques, i.e., x-ray, fluoroscopy, CT, and MRI imaging techniques. The imaging characteristics of the implant are important and getting more so. The implant should be sufficiently radiopaque to ascertain that the implant has been properly placed and to later determine that the implant stayed in its desired location and is functioning as required. It is equally important to image/identify the soft tissue adjacent to the implant for possible adverse effects, i.e., impingement against the spinal cord or nerve roots. However, materials that are highly radiopaque tend to scatter radiation and obscure the peri-prosthetic tissue. This can make it difficult to ascertain the exact location and orientation of the implant. Additionally, the scattered radiation can obscure important details of the peri-prosthetic tissues that may be important for making regional clinical diagnoses. Additionally, the desired degree of radiopacity (or radiolucency) may vary depending upon the mode of treatment, treatment site, and type of implant.
Until now, the selection of materials having varying physical and mechanical properties for medical implants has been limited. In general, traditional materials that exhibit good wear characteristics tend to have poor imaging properties. Other materials have acceptable imaging characteristics but unfavorable wear performance.
Consequently, in light of the above problems, there is a continuing need for advancements in the relevant field. These advancements include new implant designs, medical devices, and new material compositions for use in the medical field. The present invention is such an advancement and provides a variety of additional benefits and advantages.